System and method for adjusting automatic pulse parameters to selectively activate nerve fibers

ABSTRACT

A method of stimulating nerve tissue, a tissue stimulation system, and an external control device are provided. The method, system, and control device cause an electrical stimulus to be applied to at least one electrode adjacent the nerve tissue of a patient. The applied electrical stimulus comprises a plurality of pulses defined by a pulse width value and an amplitude value. The pulse amplitude value is increased (e.g., manually), and the pulse width value is automatically decreased in response to increasing the pulse amplitude value in a manner that increases the intensity of the applied electrical stimulus. Alternatively, the pulse width value may be decreased (e.g., manually), and the pulse amplitude value automatically increased in response to decreasing the pulse width value in a manner that increases the intensity of the applied electrical stimulus.

RELATED APPLICATION

The present application claims the benefit under 35 U.S.C. §119 to U.S.provisional patent application Ser. No. 61/114,951, filed Nov. 14, 2008.The foregoing application is hereby incorporated by reference into thepresent application in its entirety.

FIELD OF THE INVENTION

The present invention relates to tissue stimulation systems, and moreparticularly, to a system and method for stimulating nerve fibers.

BACKGROUND OF THE INVENTION

Implantable neurostimulation systems have proven therapeutic in a widevariety of diseases and disorders. Spinal Cord Stimulation (SCS)techniques, which directly stimulate the spinal cord tissue of thepatient, have long been accepted as a therapeutic modality for thetreatment of chronic pain syndromes, and the application of spinal cordstimulation has begun to expand to additional applications such asangina pectoralis and incontinence. In recent investigations, PeripheralStimulation (PS), which includes Peripheral Nerve Field Stimulation(PNFS) techniques that stimulate nerve tissue directly at thesymptomatic site of the disease or disorder (e.g., at the source ofpain), and Peripheral Nerve Stimulation (PNS) techniques that directlystimulate bundles of peripheral nerves that may not necessarily be atthe symptomatic site of the disease or disorder, has demonstratedefficacy in the treatment of chronic pain syndromes and incontinence,and a number of additional applications are currently underinvestigation.

These implantable neurostimulation systems typically include one or moreelectrode carrying stimulation leads, which are implanted at the desiredstimulation site, and a neurostimulator implanted remotely from thestimulation site, but coupled either directly to the stimulation lead(s)or indirectly to the stimulation lead(s) via a lead extension. Thus,electrical pulses can be delivered from the neurostimulator to thestimulation electrode(s) to stimulate or activate a volume of tissue,thereby providing the desired efficacious therapy to the patient.

The neurostimulation system may further comprise a handheld patientprogrammer to remotely instruct the neurostimulator to generateelectrical stimulation pulses in accordance with selected stimulationparameters. The handheld programmer may, itself, be programmed by atechnician attending the patient, for example, by using a Clinician'sProgrammer (CP), which typically includes a general purpose computer,such as a laptop, with a programming software package installed thereon.

Individual electrode contacts (the “electrodes”) are arranged in adesired pattern and spacing in order to create an electrode array. Thecombination of electrodes used to deliver electrical pulses to thetargeted tissue constitutes an electrode combination, with theelectrodes capable of being selectively programmed to act as anodes(positive), cathodes (negative), or left off (zero). In other words, anelectrode combination represents the polarity being positive, negative,or zero. Other parameters that may be controlled or varied includeelectrical pulse parameters, which may define the pulse amplitude(measured in milliamps or volts depending on whether constant current orconstant voltage is supplied to the electrodes), pulse width (measuredin microseconds), pulse rate (measured in pulses per second), pulseshape, and burst rate (measured as the stimulation on duration per unittime). Each electrode combination, along with the electrical pulseparameters, can be referred to as a “stimulation parameter set.” Thebest stimulus parameter set will typically be one that deliversstimulation energy to the volume of tissue that must be stimulated inorder to provide the therapeutic benefit (e.g., pain relief), whileminimizing the volume of non-target tissue that is stimulated.

Typically, the therapeutic effect for any given neurostimulationapplication may be optimized by adjusting the stimulation parameters.For example, the volume of activated tissue in any givenneurostimulation application may be increased or decreased by adjustingcertain stimulation parameters, such as amplitude and pulse width.Often, these therapeutic effects are correlated to the diameter of thenerve fibers that innervate the volume of tissue to be stimulated (i.e.,for different stimulation applications, different fiber diameters canencode different sensations).

For example, in PNFS and PNS applications, there is often a distributionof fiber diameters near the electrodes that strongly encode differentsensations. For example, the larger Abeta afferent nerve fibers in theperiphery can encode vibration and pressure, whereas the smaller Adeltanerve fibers often encode sharp pain. In these applications, if thestimulation amplitude is increased for a fixed electrode combination andpulse width, the activation of the large nerve fibers will be increasedprior to the activation of the small nerve fibers due to the inherentnature of fiber diameters and the electrical field external to the nervefibers. However, the patient may reach an amplitude limit due to theactivation of the smaller nerve fibers that generate side effects beforethe larger nerve fibers that provide the intended therapy. Thus,stimulation of the small diameter nerve fibers may lead to otheruncomfortable, painful sensations near the stimulating electrode,thereby producing side effects and limiting therapeutic coverage.Therefore, in certain stimulation applications, control of nerve fiberrecruitment based on diameter might be critically important to maximizethe therapeutic effect of the stimulation.

In contrast, in SCS applications, activation of different nerve fiberdiameters does not necessarily encode different sensations or sideeffects. In particular, in SCS, activation (i.e., recruitment) of largediameter sensory fibers in the dorsal column of the spinal cord createsa sensation known as paresthesia that can be characterized as analternative sensation that replaces the pain signals sensed within theaffected region of the patient's body. Thus, it has been believed thatthe large diameter nerve fibers are the major targets for SCS. However,the distribution of sensory nerve fiber diameters in the dorsal columnis an artifact of where the fibers enter the spinal cord and thespecific spinal cord segment stimulated. Since the nerve fibers in thedorsal column tend to be mostly sensory nerve fibers, it is generallybelieved that different fiber diameter activation merely would result inmore or less paresthesia in different parts of the patient'sbody—essentially all innocuous, if not therapeutic stimulation.Therefore, in some stimulation applications, control of nerve fiberrecruitment based on diameter might not be as critically important tomaximize the therapeutic effect of the stimulation.

Thus, there remains a need to selectively provide a means forstimulating a specific range of nerve fiber diameters over a range ofdifferent stimulation amplitude levels.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, a method ofstimulating nerve tissue (e.g., peripheral nerve tissue) is provided.The method comprises applying an electrical stimulus to at least oneelectrode adjacent the nerve tissue of a patient (e.g., during a fittingprocedure). The applied electrical stimulus comprises a plurality ofpulses defined by a pulse width value and an amplitude value. The methodmay optionally comprise implanting the electrode(s) adjacent the nervetissue.

The method further comprises increasing the pulse amplitude value (e.g.,manually), and automatically decreasing the pulse width value inresponse to increasing the pulse amplitude value in a manner thatincreases the intensity of the applied electrical stimulus.Alternatively, the method may comprise increasing the pulse width value(e.g., manually), and automatically decreasing the pulse amplitude valuein response to increasing the pulse width value in a manner thatincreases the intensity of the applied electrical stimulus. As oneexample, the pulse amplitude value and/or pulse width value can beincreased in a manner that stimulates nerve fibers of a smallerdiameter, but prevents stimulation of Adelta nerve fibers adjacent theat least one electrode. The pulse amplitude value and/or pulse widthvalue may be adjusted, e.g., by using an external control device.

In accordance with a second aspect of the present inventions, a tissuestimulation system is provided. The system comprises a pulse generatingdevice (e.g., an implantable pulse generator) for generating anelectrical stimulus having a plurality of pulses defined by a pulsewidth value and an amplitude value, and at least one electrode fordelivering the electrical stimulus to adjacent nerve tissue. The systemfurther comprises a user interface device configured for allowing a userto prompt an increase in the pulse amplitude value or prompt a decreasein the pulse width value (which may be accomplished manually), and anexternal control device configured for automatically decreasing thepulse width value in response to increasing the pulse amplitude value orautomatically increasing the pulse amplitude value in response todecreasing the pulse width value in a manner that increases theintensity of the electrical stimulus.

In accordance with a third aspect of the present inventions, an externalcontrol device for a neurostimulation device is provided. The externalcontrol device comprises a user interface capable of receiving an input(e.g., a manual input) from a user. The external control device furthercomprises a processor configured for varying an amplitude value and apulse width value of an electrical stimulus generated by a pulsegenerating device by increasing the pulse amplitude value whiledecreasing the pulse width value or decreasing the pulse width valuewhile increasing the pulse amplitude value in response to the user inputin a manner that increases the intensity of the applied electricalstimulus. The processor is further configured generating a stimulationparameter set from the varied amplitude value and pulse width value. Thepulse generating device may be programmed with the stimulation parameterset. The external control device further comprises output circuitryconfigured for transmitting the stimulation parameter set to the pulsegenerating device.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is perspective view of one embodiment of a tissue stimulationsystem arranged in accordance with the present inventions;

FIG. 2 is a side view of an implantable pulse generator and a pair ofstimulation leads that can be used in the tissue stimulation system ofFIG. 1;

FIG. 3 is a plan view of the tissue stimulation system of FIG. 1 in usewith a patient;

FIG. 4 is an exemplary plot of two strength-duration curves forrespective small diameter fibers and large diameter fibers and thevariance of a pulse amplitude and pulse width of stimulation energyrelative to the curves when the system is in a Spinal Cord Stimulation(SCS) mode;

FIG. 5 is an exemplary plot of two strength-duration curves forrespective small diameter fibers and large diameter fibers and thevariance of a pulse amplitude and pulse width of stimulation energyrelative to the curves when the system is in a Peripheral Stimulation(PS) mode;

FIG. 6 is a block diagram of the internal componentry of the IPG of FIG.2;

FIG. 7 is a plan view of a remote control that can be used in the systemof FIG. 1;

FIG. 8 is a block diagram of the internal componentry of the remotecontrol of FIG. 7;

FIG. 9 is a block diagram of the components of a computerizedprogramming system that can be used in the system of FIG. 1; and

FIG. 10 is view of a programming screen and generated by thecomputerized programming system of FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Turning first to FIG. 1, an exemplary nerve tissue stimulation system 10generally includes one or more (in this case, two) implantablestimulation leads 12, a pulse generating device in the form of animplantable pulse generator (IPG) 14, an external control device in theform of a remote controller RC 16, a clinician's programmer (CP) 18, anexternal trial stimulator (ETS) 20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the stimulation leads 12, which carry a plurality ofelectrodes 26 arranged in an array. In the illustrated embodiment, thestimulation leads 12 are percutaneous leads, and to this end, theelectrodes 26 are arranged in-line along the stimulation leads 12. Inalternative embodiments, the electrodes 26 may be arranged in atwo-dimensional pattern on a single paddle lead. As will be described infurther detail-below, the IPG 14 includes pulse generation circuitrythat delivers electrical stimulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of stimulationparameters.

The ETS 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the stimulation leads 12. The ETS20, which has similar pulse generation circuitry as that of the IPG 14,also delivers electrical stimulation energy in the form of a pulsedelectrical waveform to the electrode array 26 in accordance with a setof stimulation parameters. The major difference between the ETS 20 andthe IPG 14 is that the ETS 20 is a non-implantable device that is usedon a trial basis after the stimulation leads 12 have been implanted andprior to implantation of the IPG 14, to test the responsiveness of thestimulation that is to be provided. Further details of an exemplary ETSare described in U.S. Pat. No. 6,895,280, which is expresslyincorporated herein by reference.

The RC 16 may be used to telemetrically control the ETS 20 via abi-directional RF communications link 32. Once the IPG 14 andstimulation leads 12 are implanted, the RC 16 may be used totelemetrically control the IPG 14 via a bi-directional RF communicationslink 34. Such control allows the IPG 14 to be turned on or off and to beprogrammed with different stimulation parameter sets. The IPG 14 mayalso be operated to modify the programmed stimulation parameters toactively control the characteristics of the electrical stimulationenergy output by the IPG 14.

The CP 18 provides clinician detailed stimulation parameters forprogramming the IPG 14 and ETS 20 in the operating room and in follow-upsessions. The CP 18 may perform this function by indirectlycommunicating with the IPG 14 or ETS 20, through the RC 16, via an IRcommunications link 36. Alternatively, the CP 18 may directlycommunicate with the IPG 14 or ETS 20 via an RF communications link (notshown). For purposes of brevity and clarity, only the IPG 14 will bereferred to hereafter. The clinician detailed stimulation parametersprovided by the CP 18 are also used to program the RC 16, so that thestimulation parameters can be subsequently modified by operation of theRC 16 in a stand-alone mode (i.e., without the assistance of the CP 18).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. For purposes of brevity, thedetails of the external charger 22 will not be described herein. Detailsof exemplary embodiments of external chargers are disclosed in U.S. Pat.No. 6,895,280, which has been previously incorporated herein byreference. Once the IPG 14 has been programmed, and its power source hasbeen charged by the external charger 22 or otherwise replenished, theIPG 14 may function as programmed without the RC 16 or CP 18 beingpresent.

Referring now to FIG. 2, the external features of the stimulation leads12 and the IPG 14 will be briefly described. One of the stimulationleads 12 has eight electrodes 26 (labeled E1-E8), and the otherstimulation lead 12 has eight electrodes 26 (labeled E9-E16). The actualnumber and shape of leads and electrodes will, of course, vary accordingto the intended application. The IPG 14 comprises an outer case 40 forhousing the electronic and other components (described in further detailbelow), and a connector 42 to which the proximal ends of the stimulationleads 12 mate in a manner that electrically couples the electrodes 26 tothe internal electronics (described in further detail below) within theouter case 40. The outer case 40 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case40 may serve as an electrode.

As briefly discussed above, the IPG 14 includes battery and pulsegeneration circuitry that delivers the electrical stimulation energy inthe form of a pulsed electrical waveform to the electrode array 26 inaccordance with a set of stimulation parameters programmed into the IPG14. Such stimulation parameters may comprise electrode combinations,which define the electrodes that are activated as anodes (positive),cathodes (negative), and turned off (zero), percentage of stimulationenergy assigned to each electrode (fractionalized electrodeconfigurations), and electrical pulse parameters, which define the pulseamplitude (measured in milliamps or volts depending on whether the IPG14 supplies constant current or constant voltage to the electrode array26), pulse width (measured in microseconds), and pulse rate (measured inpulses per second).

Electrical stimulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case. Simulation energy may betransmitted to the tissue in a monopolar or multipolar (e.g., bipolar,tripolar, etc.) fashion. Monopolar stimulation occurs when a selectedone of the lead electrodes 26 is activated along with the case of theIPG 14, so that stimulation energy is transmitted between the selectedelectrode 26 and case. Bipolar stimulation occurs when two of the leadelectrodes 26 are activated as anode and cathode, so that stimulationenergy is transmitted between the selected electrodes 26. For example,electrode E3 on the first lead 12 may be activated as an anode at thesame time that electrode E11 on the second lead 12 is activated as acathode. Tripolar stimulation occurs when three of the lead electrodes26 are activated, two as anodes and the remaining one as a cathode, ortwo as cathodes and the remaining one as an anode. For example,electrodes E4 and E5 on the first lead 12 may be activated as anodes atthe same time that electrode E12 on the second lead 12 is activated as acathode.

The stimulation energy may be delivered between electrodes as monophasicelectrical energy or multiphasic electrical energy. Monophasicelectrical energy includes a series of pulses that are either allpositive (anodic) or all negative (cathodic). Multiphasic electricalenergy includes a series of pulses that alternate between positive andnegative. For example, multiphasic electrical energy may include aseries of biphasic pulses, with each biphasic pulse including a cathodic(negative) stimulation pulse and an anodic (positive) recharge pulsethat is generated after the stimulation pulse to prevent direct currentcharge transfer through the tissue, thereby avoiding electrodedegradation and cell trauma. That is, charge is conveyed through theelectrode-tissue interface via current at an electrode during astimulation period (the length of the stimulation pulse), and thenpulled back off the electrode-tissue interface via an oppositelypolarized current at the same electrode during a recharge period (thelength of the recharge pulse).

For spinal cord stimulation (SCS) applications, the electrode leads 12are implanted within the spinal column 52 of a patient 50, as shown inFIG. 3. For spinal cord stimulation (SCS) applications, the preferredplacement of the electrode leads 12 is adjacent, i.e., resting near, orupon the dura, adjacent to the spinal cord area to be stimulated. Forperipheral stimulation (PS) applications, the electrode leads 12 areimplanted remotely from the spinal cord; for example, subcutaneously inthe lower back (not shown in FIG. 3) or any other region whereperipheral nerves can be stimulated. For the purposes of thisspecification, peripheral nerve tissue is any nerve tissue that is notpart of the central nervous system (i.e., nerve tissue other than thebrain or spinal cord). The IPG 14 is generally implanted in asurgically-made pocket either in the abdomen or above the buttocks. TheIPG 14 may, of course, also be implanted in other locations of thepatient's body. The lead extension 24 facilitates locating the IPG 14away from the electrode leads 12. As there shown, the CP 18 communicateswith the IPG 14 via the RC 16.

Significant to the present inventions, the tissue stimulation system 10can be selectively operated between a spinal cord stimulation (SCS) mode(FIG. 4) and a peripheral stimulation (PS) mode (FIG. 5). In both modes,the intensity of the electrical energy conveyed through the target nervetissue can be increased by adjusting the pulse amplitude and/or pulsewidth of the electrical energy relative to strength-duration curves,which represent the pulse amplitude and pulse width needed to stimulatenerve fibers of specified diameters. As shown in FIGS. 4 and 5, S-Dcurve 1 represents the strength-duration curve for a relatively smallnerve fiber, whereas S-D curve 2 represents the strength-duration curvefor a relatively large nerve fiber.

In the SCS mode, the system 10 increases the intensity of electricalenergy relatively quickly, thereby stimulating nerves of decreasinglysmaller diameters relatively quickly. Because the nerve fibers in thedorsal column tend to be mostly sensory nerve fibers, the activation ofdifferent fiber diameters is essentially innocuous, and therefore, itmay be advantageous to recruit as many nerve fibers—albeit withdifferent diameters, as possible to provide for a more efficientprogramming process.

In the illustrated embodiment, the system 10, when in the SCS mode,allows a user to manually increase the pulse amplitude of the electricalenergy or automatically increases the pulse amplitude of the electricalenergy without modifying the pulse width the electrical energy, as shownby Line A in FIG. 4. Alternatively, the system 10 allows a user tomanually increase the pulse amplitude of the electrical energy whileautomatically increasing the pulse width of the electrical energy,allows a user to manually increase the pulse width of the electricalenergy while automatically increasing the pulse amplitude of theelectrical energy, or automatically increases both the pulse amplitudeand pulse width of the electrical energy, as shown by Line B. Furtherdetails discussing techniques for increasing both the pulse amplitudeand pulse width of electrical energy are provided in U.S. Pat. No.7,174,215, which is expressly incorporated herein by reference.Alternatively, the system 10 allows a user to manually increase thepulse width of the electrical energy or automatically increases thepulse width of the electrical energy without modifying the pulseamplitude of the electrical energy, as shown by Line C.

In the PS mode, the system 10 increases the intensity of electricalenergy relatively gradually, thereby stimulating nerves of decreasinglysmaller diameters gradually, relative to more distal, larger diameternerves. Because the peripheral nerves typically include smaller Adeltanerve fibers that encode sharp pain, it is desirable that the intensityof the electrical energy be increased gradually.

In the illustrated embodiment, the system 10, when in the PS mode,allows a user to increase the intensity of the stimulation. Inparticular, the system 10 allows the user to manually increase the pulseamplitude of the electrical energy while automatically decreasing thepulse width of the electrical energy, allows a user to manually decreasethe pulse width of the electrical energy while automatically increasingthe pulse amplitude of the electrical energy, and/or automaticallyincreases the pulse amplitude while automatically decreasing the pulsewidth of the electrical energy, as shown by Line D in FIG. 5. Althoughthe manual decrease of the pulse width is usually not associated with anincrease in stimulation intensity, the accompanying increase the pulseamplitude will effect the increase in the stimulation intensity.Notably, although all three these adjustments increases the intensity ofthe electrical energy, thereby potentially activating Adelta nervefibers, the decreasing of the pulse width takes advantage of theincreasing threshold difference between smaller and larger nerve fiberswith the decreasing pulse width (See P. H. Gorman and J. T. Mortimer,“The effect of stimulus parameters on the recruitment characteristics ofdirect nerve stimulation,” IEEE Trans. Biomed. Eng., vol. 30, pp.407-414, July 1983). As a result, it may be easier to gradually recruitthe smaller innocuous nerve fibers without activating the pain carryingAdelta nerve fibers.

Notably, the offset of the pulse amplitude-pulse width curve D can beadjusted to set the initial nerve diameter that is stimulated by theelectrical energy. For example, the offset can be increased, as shown byLine D1, or the offset can be decreased, as shown by Line D2. The shapeof the pulse amplitude-pulse width Line D can also be adjusted toincrease or decrease the rate at which the intensity of the electricalenergy is increased. For example, the rate at which the intensity of theelectrical energy is changed can be increased, as shown by Line D3(shown in phantom), or the rate at which the intensity of the electricalenergy is changed can be decreased, as shown by Line D4 (shown inphantom).

Although the pulse amplitude and pulse width of the electrical energyoutput by the IPG 14 may be controlled by either the RC 16 or the CP 18,the CP 18 is described herein as having the means for adjusting thepulse amplitude and pulse width.

Turning next to FIG. 6, the main internal components of the IPG 14 willnow be described. The IPG 14 includes analog output circuitry 60configured for generating electrical stimulation energy in accordancewith a defined pulsed waveform having a specified pulse amplitude, pulserate, pulse width, and pulse shape under control of control logic 62over data bus 64. Control of the pulse rate and pulse width of theelectrical waveform is facilitated by timer logic circuitry 66, whichmay have a suitable resolution, e.g., 10 μs. The stimulation energygenerated by the analog output circuitry 60 is output via capacitorsC1-C16 to electrical terminals 68 corresponding to electrodes E1-E16.

The analog output circuitry 60 may either comprise independentlycontrolled current sources for providing stimulation pulses of aspecified and known amperage to or from the electrical terminals 68, orindependently controlled voltage sources for providing stimulationpulses of a specified and known voltage at the electrical terminals 68or to multiplexed current or voltage sources that are then connected tothe electrical terminals 68. The operation of this analog outputcircuitry, including alternative embodiments of suitable outputcircuitry for performing the same function of generating stimulationpulses of a prescribed amplitude and width, is described more fully inU.S. Pat. Nos. 6,516,227 and 6,993,384, which are expressly incorporatedherein by reference. The analog output circuitry 60 may also comprisepulse shaping circuitry (not shown) capable of shaping the pulses (e.g.,a square pulse, an exponential pulse, a logarithmic pulse, a rampedpulse, a trapezoidal pulse, etc.). Further details discussing pulseshaping circuitry and the different pulse shapes that can be generatedare disclosed in U.S. Patent Application Ser. No. 60/951,177, entitled“Use of Stimulation Pulse Shape to Control Neural Recruitment Order andClinical Effect,” which is expressly incorporated herein by reference.

The IPG 14 further comprises monitoring circuitry 70 for monitoring thestatus of various nodes or other points 72 throughout the IPG 14, e.g.,power supply voltages, temperature, battery voltage, and the like. Themonitoring circuitry 70 is also configured for measuring electricalparameter data (e.g., electrode impedance and/or electrode fieldpotential). The IPG 14 further comprises processing circuitry in theform of a microcontroller (μC) 74 that controls the control logic 62over data bus 76, and obtains status data from the monitoring circuitry70 via data bus 78. The IPG 14 further comprises memory 80 andoscillator and clock circuit 82 coupled to the μC 74. The μC 74, incombination with the memory 80 and oscillator and clock circuit 82, thuscomprise a microprocessor system that carries out a program function inaccordance with a suitable program stored in the memory 80.Alternatively, for some applications, the function provided by themicroprocessor system may be carried out by a suitable state machine.

Thus, the μC 74 generates the necessary control and status signals,which allow the μC 74 to control the operation of the IPG 14 inaccordance with a selected operating program and stimulation parameters.In controlling the operation of the IPG 14, the μC 74 is able toindividually generate stimulus pulses at the electrical terminals 68using the analog output circuitry 60, in combination with the controllogic 62 and timer logic circuitry 66, thereby allowing each electricalterminal 68 to be paired or grouped with other electrical terminals 68,including the monopolar case electrode, to control the polarity,amplitude, rate, pulse width, pulse shape, and channel through which thecurrent stimulus pulses are provided. The μC 74 facilitates the storageof electrical parameter data measured by the monitoring circuitry 70within memory 80.

The IPG 14 further comprises a receiving coil 84 for receivingprogramming data (e.g., the operating program and/or stimulationparameters) from the external programmer (i.e., the RC 16 or CP 18) inan appropriate modulated carrier signal, and charging, and circuitry 86for demodulating the carrier signal it receives through the receivingcoil 84 to recover the programming data, which programming data is thenstored within the memory 80, or within other memory elements (not shown)distributed throughout the IPG 14.

The IPG 14 further comprises back telemetry circuitry 88 and atransmission coil 90 for sending informational data to the externalprogrammer. The back telemetry features of the IPG 14 also allow itsstatus to be checked. For example, when the CP 18 initiates aprogramming session with the IPG 14, the capacity of the battery istelemetered, so that the CP 18 can calculate the estimated time torecharge. Any changes made to the current stimulus parameters areconfirmed through back telemetry, thereby assuring that such changeshave been correctly received and implemented within the implant system.Moreover, upon interrogation by the CP 18, all programmable settingsstored within the IPG 14 may be uploaded to the CP 18.

The IPG 14 further comprises a rechargeable power source 92 and powercircuits 94 for providing the operating power to the IPG 14. Therechargeable power source 92 may, e.g., comprise a lithium-ion orlithium-ion polymer battery or other form of rechargeable power. Therechargeable source 92 provides an unregulated voltage to the powercircuits 94. The power circuits 94, in turn, generate the variousvoltages 96, some of which are regulated and some of which are not, asneeded by the various circuits located within the IPG 14. Therechargeable power source 92 is recharged using rectified AC power (orDC power converted from AC power through other means, e.g., efficientAC-to-DC converter circuits) received by the receiving coil 84.

To recharge the power source 92, the external charger 22 (shown in FIG.1), which generates the AC magnetic field, is placed against, orotherwise adjacent, to the patient's skin over the implanted IPG 14. TheAC magnetic field emitted by the external charger induces AC currents inthe receiving coil 84. The charging and forward telemetry circuitry 86rectifies the AC current to produce DC current, which is used to chargethe power source 92. While the receiving coil 84 is described as beingused for both wirelessly receiving communications (e.g., programming andcontrol data) and charging energy from the external device, it should beappreciated that the receiving coil 84 can be arranged as a dedicatedcharging coil, while another coil, such as the coil 90, can be used forbi-directional telemetry.

Additional details concerning the above-described and other IPGs may befound in U.S. Pat. No. 6,516,227, U.S. Patent Publication No.2003/0139781, and U.S. patent application Ser. No. 11/138,632, entitled“Low Power Loss Current Digital-to-Analog Converter Used in anImplantable Pulse Generator,” which are expressly incorporated herein byreference.

It should be noted that rather than an IPG, the SCS system 10 mayalternatively utilize an implantable receiver-stimulator (not shown)connected to the stimulation leads 12. In this case, the power source,e.g., a battery, for powering the implanted receiver, as well as controlcircuitry to command the receiver-stimulator, will be contained in anexternal controller inductively coupled to the receiver-stimulator viaan electromagnetic link. Data/power signals are transcutaneously coupledfrom a cable-connected transmission coil placed over the implantedreceiver-stimulator. The implanted receiver-stimulator receives thesignal and generates the stimulation in accordance with the controlsignals.

Referring now to FIG. 7, one exemplary embodiment of an RC 16 will nowbe described. As previously discussed, the RC 16 is capable ofcommunicating with the IPG 14 or CP 18. The RC 16 comprises a casing100, which houses internal componentry (including a printed circuitboard (PCB)), and a lighted display screen 102 and button pad 104carried by the exterior of the casing 100. In the illustratedembodiment, the display screen 102 is a lighted flat panel displayscreen, and the button pad 104 comprises a membrane switch with metaldomes positioned over a flex circuit, and a keypad connector connecteddirectly to a PCB. In an optional embodiment, the display screen 102 hastouchscreen capabilities. The button pad 104 includes a multitude ofbuttons 106, 108, 110, and 112, which allow the IPG 14 to be turned ONand OFF, provide for the adjustment or setting of stimulation parameterswithin the IPG 14, and provide for selection between screens.

In the illustrated embodiment, the button 106 serves as an ON/OFF buttonthat can be actuated to turn the IPG 14 ON and OFF. The button 108serves as a select button that allows the RC 16 to switch between screendisplays and/or parameters. The buttons 110 and 112 serve as up/downbuttons that can actuated to increment or decrement any of stimulationparameters of the pulse generated by the IPG 14, including pulseamplitude, pulse width, and pulse rate. For example, the selectionbutton 108 can be actuated to place the RC 16 in an “Pulse AmplitudeAdjustment Mode,” during which the pulse amplitude can be adjusted viathe up/down buttons 110, 112, a “Pulse Width Adjustment Mode,” duringwhich the pulse width can be adjusted via the up/down buttons 110, 112,and a “Pulse Rate Adjustment Mode,” during which the pulse rate can beadjusted via the up/down buttons 110, 112. Optionally, the RC 16 may beplaced in a “Pulse Shaping Adjustment Mode,” which is described infurther detail in U.S. Patent Application Ser. No. 60/951,177, which waspreviously incorporated herein by reference.

Alternatively, dedicated up/down buttons can be provided for eachstimulation parameter. Rather than using up/down buttons, any other typeof actuator, such as a dial, slider bar, or keypad, can be used toincrement or decrement the stimulation parameters. Further details ofthe functionality and internal componentry of the RC 16 are disclosed inU.S. Pat. No. 6,895,280, which has previously been incorporated hereinby reference.

Referring to FIG. 8, the internal components of an exemplary RC 16 willnow be described. The RC 16 generally includes a processor 114 (e.g., amicrocontroller), memory 116 that stores an operating program forexecution by the processor 114, as well as stimulation parameter sets(which can be generated from a look-up table or a formula), input/outputcircuitry, and in particular, telemetry circuitry 118 for outputtingstimulation parameters to the IPG 14 and receiving status informationfrom the IPG 14, and input/output circuitry 120 for receivingstimulation control signals from the button pad 104 and transmittingstatus information to the display screen 102 (shown in FIG. 7). As wellas controlling other functions of the RC 16, which will not be describedherein for purposes of brevity, the processor 114 generates newstimulation parameter sets in response to the user operation of thebutton pad 104. These new stimulation parameter sets would then betransmitted to the IPG 14 via the telemetry circuitry 118. Furtherdetails discussing the functionality and internal componentry of the RC16 are disclosed in U.S. Pat. No. 6,895,280, which has previously beenincorporated herein by reference.

As briefly discussed above, the CP 18 greatly simplifies the programmingof multiple electrode combinations, allowing the physician or clinicianto readily determine the desired stimulation parameters to be programmedinto the IPG 14, as well as the RC 16. Thus, modification of thestimulation parameters in the programmable memory of the IPG 14 afterimplantation is performed by a clinician using the CP 18, which candirectly communicate with the IPG 14 or indirectly communicate with theIPG 14 via the RC 16. That is, the CP 18 can be used by the physician orclinician to modify operating parameters of the electrode array 26 nearthe spinal cord.

As shown in FIG. 3, the overall appearance of the CP 18 is that of alaptop personal computer (PC), and in fact, may be implemented using aPC that has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. Thus, the programming methodologies can be performedby executing software instructions contained within the CP 18.Alternatively, such programming methodologies can be performed usingfirmware or hardware. In any event, the CP 18, under the control of theclinician, may actively control the characteristics of the electricalstimulation generated by the IPG 14 to allow the optimum stimulationparameters to be determined based on patient feedback and forsubsequently programming the IPG 14 with the optimum stimulationparameters.

As shown in FIG. 9, the CP 18 generally includes a processor 130 (e.g.,a central processor unit (CPU)) and memory 132 that stores a stimulationprogramming package 134, which can be executed by the processor 130 toallow a clinician to program the IPG 14 and RC 16. The memory 132 alsostores data defining various pulse amplitude-pulse width lines (such asthose illustrated in FIGS. 4 and 5). In performing this function, theprocessor 130 generates a plurality of stimulation parameter sets fromthe parameter values manually varied by the user via operation of theuser input device 122, 124, or otherwise automatically varied by theprocessor 130 itself. The CP 18 further includes output circuitry 136(e.g., via the telemetry circuitry of the RC 16) for downloadingstimulation parameters to the IPG 14 and RC 16 and for uploadingstimulation parameters already stored in the memory 116 of the RC 16,via the telemetry circuitry 118 of the RC 16. To allow the clinician toperform these functions, the CP 18 includes a user input device (e.g., amouse 122 and keyboard 124 shown in FIG. 3), and a display monitor 126housed in a case 128 (also shown in FIG. 3).

Further details discussing user interfaces and exemplary stimulationprogramming packages are described in U.S. Pat. No. 6,393,325 and U.S.Patent Application Ser. No. 61/080,187, entitled “System and Method forConverting Tissue Stimulation Programs in a Format Usable by anElectrical Current Steering Navigator,” which are expressly incorporatedherein by reference.

An example of a programming screen 150 that can be generated by the CP18 is shown in FIG. 10. The programming screen 150 allows a user toperform automated stimulation parameter testing, manual stimulationparameter testing, and electrode combination selection functions.

The programming screen 150 includes various stimulation parameterentries that define the ranges of stimulation parameters to beautomatically tested. In particular, the programming screen includes apulse width entry 152 (expressed in microseconds (μs)), a pulse rateentry 154 (expressed in Hertz (Hz)), and a pulse amplitude entry 156(expressed in milliamperes (mA)). The user may enter a “begin” value andan “end” value for each stimulation parameter to be automaticallyadjusted. In one embodiment, only a single parameter (e.g., pulse widthentry 152) is highlighted to be auto-adjusted. The programming screen150 also includes a start button 158, which begins the automaticadjustment of the highlighted stimulation parameter from its “begin”value through a minimum increment to its “end” value, and a stop button160, which halts the automatic adjustment of the highlighted stimulationparameter. The programming screen 150 also includes a pacing control162, the left arrow of which can be clicked to decrease the speed of theparameter adjustment and the right arrow of which can be clicked toincrease the speed of the parameter adjustment.

The programming screen 150 also includes various stimulation parametercontrols that can be operated by the user to manually adjust stimulationparameters. In particular, the programming screen 150 includes a pulsewidth adjustment control 164 (expressed in microseconds (μs)), a pulserate adjustment control 166 (expressed in Hertz (Hz)), and a pulseamplitude adjustment control 168 (expressed in milliampheres (mA)). Eachcontrol includes a first arrow that can be clicked to decrease the valueof the respective stimulation parameter and a second arrow that can beclicked to increase the value of the respective stimulation parameter.The programming screen 150 also includes multipolar/monopolarstimulation selection control 170, which includes check boxes that canbe alternately clicked by the user to provide multipolar or monopolarstimulation.

The programming screen 150 also includes an electrode combinationcontrol 172 having arrows that can be clicked by the user to select oneof three different electrode combinations 1-3. Each of the electrodecombinations 1-3 can be conventionally created either manually; forexample, clicking on selected electrodes of a graphical electrode array(not shown) as anodes and cathodes and defining a percentage anodiccurrent or cathodic current for each selected electrode (e.g., turningoff electrode E1 as an anode, and turning on electrode E2 as an anode,and defining an anodic current for electrode E2), or automatically; forexample, by gradually shifting current between anodic ones of theelectrodes and/or gradually shifting current between cathodic ones ofthe electrodes via a directional device, such as a joystick or mouse(e.g., shifting anodic electrical current from electrode E1 to electrodeE2 in 5% increments).

The programming screen 150 comprises a pulse amplitude-pulse width autoadjust control 174, which includes check boxes that can be alternatelyclicked by the user to selectively place the system 10 between an SCSmode (no auto adjust) and a PS mode (auto adjust), as described abovewith respect to FIGS. 4 and 5. Alternatively, as another example, theauto-adjust control 174 may be incorporated into the programminginterface device as a button or key that is pressed when activated andthen depressed when released, such as an Alt key. Other examples areeasily incorporated into a parameter adjustment screen. The programmingscreen 150 further includes an offset adjustment control 176 havingarrows that can be clicked by the user to vary the offset of the pulseamplitude-pulse width line (e.g., Lines D1 and D2 in FIG. 5), and a lineshaping adjustment control 178 having arrows that can be clicked by theuser to increase or decrease the rate at which the intensity isincreased (e.g., Lines D3 and D4 in FIG. 5). The programming screen 150further comprises a stimulation on/off control 180 that can bealternately clicked to turn the stimulation on or off.

When the system 10 is in the SCS mode by clicking the No Auto Adjustcheck box in the auto-adjust control 174, the user may click the startbutton 158, so that the pulse amplitude value and/or pulse width valueare automatically increased to quickly increase the intensity of theresulting electrical energy (e.g., such that the pulse amplitude valuesand/or pulse width values follow one of Lines A-C illustrated in FIG.4). If both the pulse amplitude value and the pulse width value are tobe automatically increased (as in Line B), only the “begin” value and“end” value of the pulse amplitude need be entered by the user, and the“begin” value and “end” value of pulse width will be automaticallypopulated in accordance with a predefined curve.

Alternatively, the user may manually adjust the amplitude value and/orpulse width value when the system 10 is in the SCS mode. In this case,the pulse amplitude value can be manually increased or the pulse widthvalue can be manually decreased via operation of the controls 164, 168(e.g., such that the pulse amplitude values or pulse width values followone of Lines A and C illustrated in FIG. 4), or alternatively, the pulseamplitude value can be manually increased via operation of the control168 and the pulse width value automatically increased (e.g., such thatthe pulse amplitude values and pulse width values follow Line Billustrated in FIG. 4).

When the system 10 is in the PS mode by clicking the Auto Adjust checkbox in the auto-adjust control 174, the user may click the start button158, so that the pulse amplitude value is automatically increased, andthe pulse width value is automatically decreased to slowly increase theintensity of the resulting electrical energy (e.g., such that the pulseamplitude values and pulse width values follow Line D illustrated inFIG. 5). In this case, the “begin” value of pulse amplitude need only beentered by the user, and the “end” value of the pulse amplitude and the“begin” and “end” values of the pulse width will be automaticallypopulated, or the “begin” value of the pulse width need only be enteredby the user, and the “end” value of the pulse width and the “begin” and“end” values of the pulse amplitude will be automatically populated.

Alternatively, the user may manually adjust the amplitude value or thepulse width value when the system 10 is in the PS mode. In this case,the pulse amplitude value can be manually increased via operation of thecontrol 168 and the pulse width value automatically decreased, or thepulse width value can be manually decreased via operation of the control164 and the pulse amplitude value automatically increased (e.g., suchthat the pulse amplitude values and pulse width values follow Line Dillustrated in FIG. 5).

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

What is claimed is:
 1. A method of stimulating nerve tissue, comprising: applying an electrical stimulus to at least one electrode adjacent the nerve tissue of a patient, the applied electrical stimulus comprising a plurality of pulses defined by a pulse width value and an amplitude value; increasing the pulse amplitude value or decreasing the pulse width value; and automatically decreasing the pulse width value in response to increasing the pulse amplitude value or automatically increasing the pulse amplitude value in response to decreasing the pulse width value in a manner that increases the intensity of the applied electrical stimulus.
 2. The method of claim 1, wherein the pulse amplitude value is increased, and the pulse width value is automatically decreased in response to increasing the pulse amplitude value.
 3. The method of claim 1, wherein the pulse width is decreased, and the pulse amplitude value is automatically increased in response to decreasing the pulse width value is decreased.
 4. The method of claim 1, wherein the nerve tissue is peripheral nerve tissue.
 5. The method of claim 1, wherein the pulse width value is automatically decreased in response to increasing the pulse amplitude value or the pulse amplitude value is automatically increased in response to decreasing the pulse width value in a manner that prevents stimulation of Adelta nerve fibers adjacent the at least one electrode.
 6. The method of claim 1, wherein the pulse width value is automatically decreased or the pulse amplitude value is automatically increased in a manner that stimulates nerve fibers of a smaller diameter.
 7. The method of claim 1, wherein the electrical stimulus is applied by an implanted pulse generating device, and the pulse amplitude value and pulse width value are adjusted by an external control device.
 8. The method of claim 1, wherein the pulse amplitude value is increased manually or the pulse width is decreased manually.
 9. The method of claim 1, further comprising implanting the at least one electrode within the patient in contact with the tissue.
 10. The method of claim 1, wherein the electrical stimulus is applied to the at least one electrode during a fitting procedure. 